1. Field of the Invention
The present invention relates to an organic light emitting device and a manufacturing process for the same, and more particularly, to an organic light emitting device used as a multi-color light emitting device for use in flat panel displays, projection displays, printers, etc., and to a manufacturing process for the same.
2. Description of the Related Art
In recent years, self-light emitting devices for flat panels are attracting attention. The self-light emitting devices include plasma light emitting display devices, field emission devices and organic light emitting devices (electroluminescence (EL) devices).
As for the organic light emitting devices, in particular, T. W. Tang et al. verified in 1987 that high-intensity light emission can be obtained by low-voltage DC drive, making use of the structure of a laminate formed of a film of a fluorescent metal chelate complex and a thin film of diamine-based molecules, and research and development thereof are under way energetically.
The objects of the research and development of the organic light emitting device include a reduction in drive voltage, an improvement of light extraction efficiency and an improvement of drive deterioration characteristics. As means for attaining those objects, there are conventionally known prior art technologies for doping an electron injecting material into an organic compound layer.
That is, there is known a technology for reducing the drive voltage by using an electron transporting material and an alkali metal, alkali salt or alkali oxide as the materials of an electron injecting and transporting layer (refer to Japanese Patent Application Laid-Open No. 10-270171 and Japanese Patent Application Laid-Open No. 10-270172). There is also known a technology for reducing the drive voltage by providing a concentration gradient in which an amount of an electron injecting material is large on a side near a cathode and increases as a distance from a cathode becomes larger (refer to Japanese Patent Application Laid-Open No. 2002-313583). There is further known a technology for suppressing the deterioration with time by using a mixed layer of cesium carbonate and an electron transporting material which can be easily handled as an electron injecting and transporting layer, and by setting the concentration of a dopant in the layer to 8 wt % or less (refer to Japanese Patent Application Laid-Open No. 2005-63910).
However, as the result of studies of the inventor of the present invention, it has been found that doping an electron transporting material with an electron injection dopant material such as an alkali metal, or a salt or an oxide thereof in a high concentration induces a reduction in light extraction efficiency though it has the effect of reducing the drive voltage.